Cleft lip and palate is a common congenital anomaly with significant lifelong morbidity. The extensive psychological, surgical, speech and dental involvement emphasize the importance of understanding the underlying causes. Our long-term objective is to discover the genes and environmental factors that contribute to this disorder. However, the etiology of cleft lip and palate is complex, and given the large number of genes predicted to be involved in isolated cleft lip and palate, gene discovery poses a significant challenge. The approach used here will be to study a genetically simple model of orofacial clefting, Van der Woude syndrome. Van der Woude syndrome is an outstanding clinical model for isolated cleft lip and palate, as its only distinguishing features are pits in the lower lip. Mutations in Interferon Regulatory Factor 6 (IRF6) cause Van der Woude syndrome. Moreover, genetic variation in IRF6 confers risk for isolated cleft lip and palate, demonstrating that Van der Woude syndrome is also an outstanding genetic model. Thus, IRF6 is essential for a critical pathway in palate development, and its discovery represents a foothold in this pathway. The main goal of this proposal is to delineate the IRF6 pathway by first determining the in vivo function of IRF6 and then identifying factors that regulate the expression of IRF6. There are 3 Aims: 1) To generate a mouse model for Van der Woude syndrome by mutating Irf6, and to perform a comprehensive analysis of the pathogenic processes in palate development in these mice. To investigate a role for Type I interferons in palate development in mice, as IRF6 is a member of the Interferon Regulatory family of transcription factors. 2) To evaluate a potential genetic interaction between mutations in Irf6 and Transformation growth factor beta3 (Tgfbeta3), since Tgfa3 is necessary for palate development and for Irf6 expression in the palate. Mice that are double heterozygotes for Irf6 and Tgfbeta3 will be analyzed for palate development. Also, to examine the potential role for Irf6 in transducing the Tgfbeta3 signal during palate development. 3) To identify the enhancer that regulates Irf6 expression in the palate using transgenic mice. Does Tgfbeta3 regulate Irf6 through the SMADs or by other transcription factors or both? Completion of these aims will advance our understanding for the role of IRF6 in palate development, and identify novel gene interactions and genes that may contribute to isolated cleft lip and palate, a common human disorder. This knowledge will provide the basis for enhanced diagnostic tests and future preventive interventions.